The reservoir pressure of most oil wells is insufficient to force the formation fluid to free flow from the bottom of the borehole, up the tubing string, and to the surface of the ground. It is therefore necessary to rely upon artificial lift means in order to produce most oil wells. This is usually accomplished with a pumpjack unit having a string of sucker rods extending downhole in a cased wellbore for reciprocating a downhole pump. Apparatus such as this has been used for many years. The well casing, downhole pump, production tubing, and string of sucker rod are all placed in intimate contact with the well fluids.
The well fluids usually are very corrosive and accordingly these expensive mechanical components are subjected to the deleterious effects of the corrosive liquid and gas produced by the oil well. For this reason, from time to time, it is advantageous to treat the borehole with a corrosion inhibiting compound. It would, therefore, be desirable to measure the rate of corrosion that occurs downhole in a borehole in order to enable the reservoir engineer to ascertain the appropriate amount of inhibitor to add to the borehole.
The determination of the rate of corrosion that occurs on the production equipment used downhole in a wellbore is the subject of the present invention.